Sorry to say but hands down, this is the most confusing part of the solution. If you can guide your way out of this section, then the rest will just be a walk through the park.
The remaining 8 outeredges are already on the bottom layer, and chances are they are pretty much scrambled. The first step is to arrange them in the correct positions. Randomly choose a front side, and proceed to solve the back edges; starting with the backleft edge first and the backright edge second.
Note: these diagrams look strange. The first one appears to take 4 outeredges and cram them into one. What the first diagram actually means is that if an outeredge cube is coming from the left or right sides, then you must repeat the sequence until it appears in the backleft edge. You may have to repeat this sequence four times before that happens.
The second diagram represents any outeredge from the front side moving to the backleft edge. You may have to repeat that squence twice before it lands there. The dark squares on both diagrams are edges cubes that do not move at all during the process.
Now continue to...
~~~~ Move an OuterEdge to the BackLeft ~~~~ 

______________________________ 

Move an edge

Repeat the 
...until the edge lands


M B M+ B2

You may have to 

Bottom View 

______________________________ 

Move an edge

Repeat the 
...until the edge lands


M B2 M+ B 
You may have to 

Bottom View 
~~~~ Move an OuterEdge to the BackRight: ~~~~ 

______________________________ 

Move an edge

Repeat the 
...until the edge lands


O B+ O+ B2

You may have to 

Bottom View 

______________________________ 

Move an edge

Repeat the 
...until the edge lands


O B2 O+ B+ 
You may have to 

Bottom View 
If you are lucky, the outeredges going to the back are already paired. You can still move them one at a time, or you can use these shortcuts:
~~~~ Move an EdgePair ~~~~ 

...from the left: 
...from the front: 
...from the right: 

Bottom View 
Bottom View 
Bottom View 

O B+ O+ B2 
M M B2 
M B M+ B2 
All sequences only have to be performed once to accomplish the move.
Both back edges should now be in place... 
...rotate the entire puzzle so that the fixed edges are in the front... 
...and solve the "other" back side. 
Once again, you have to use the same sequences as before, except this time, the outeredges are coming from the sides only.
Move a single

Move a single

Swap the left

Swap the right


Bottom View 
Bottom View 
Bottom View 
Bottom View 

M B M+ B2 
O B+ O+ B2 
O B+ O+ B2

M B M+ B2

The back and front edges are now in place.... 
...rotate the entire puzzle so that the fixed edges are on the sides... 
...and solve the back side again. 
This time, you only have to use the sequences that move the outeredges from the front to the back:
Move a single

Move a single

Swap the front


M B2 M+ B

O B2 O+ B+

M M B2 
Once you solve the back side (for the third time), the remaining 2 outeredges are forced to the front side, where they belong! Therefore, all 8 bottom outeredges are in place. Now for the next step: INVERSION.
There are 5 different inversion schemes:
For each inversion scheme, you must rotate the entire puzzle so that the inverted edgepairs are positioned exactly like the ones in the diagrams, before attempting the sequence of moves!
~~~~ Case #1: Invert two adjacent edgepairs ~~~~ 

[MNO] B [MNO]+ B 
Result: 

______________________________ 

~~~~ Case #2: Invert two opposite edgepairs ~~~~ 

[MNO] B [MNO]+ B 
Result: 

______________________________ 

~~~~ Case #3: Invert four edgepairs ~~~~ 

[MNO] B [MNO]+ B 
Result: 

______________________________ 

~~~~ Case #4: Invert three edgepairs ~~~~ 

M B M B2 
Result: 

______________________________ 

~~~~ Case #5: Invert one edgepair ~~~~ 

M B M B2 
Result: 
As it turns out, only two different sequences were used throughout all five cases.
Now that the bottom outeredges are solved, the next thing to tackle are the
Bottom InnerEdges.